SUMMARY Dr. Rusconi has a long-standing interest in host microbial interactions. Her work has focused on infants born preterm, who are exceptionally prone to life-threatening gut-associated pathology, most notably necrotizing enterocolitis (NEC). The absence of preventive strategies for NEC and its abysmal outcomes, compelled Dr. Rusconi to perform a broad range metabolomics analysis of pre-event NEC specimens to better understand its pathophysiology. A unique sphingolipid profile emerged, which was confirmed in a larger cohort by targeted mass spectrometry. Sphingolipids perform diverse functions in the human body. Sphingosine-1-phosphate (S1P), a sphingolipid metabolite, is an important signaling molecule that promotes lymphocyte migration. The sensing of S1P by S1P receptor 1 (S1P1) is antagonized in vivo by multiple S1P1 agonists, such as SEW2871, through the internalization and degradation of the receptor. By treating neonatal mice with SEW2871 she observed the predicted systemic lymphopenia and and increase in dendritic and T cells in the small intestine lamina propria. The accumulation of these cells in the lamina propria was not observed in adult mice. Aim 1 will focus on identifying age-specific functional responses of the small intestinal lamina propria upon S1P antagonism. Dr. Rusconi will complement pharmacological data with cell-type specific S1P1 KO mice to address cell-specific requirements. The sphingolipid signature and dysbiosis appear in the same pre-NEC interval. Aim 2 focuses on determining their relationship. Germ-free mice will be colonized with dysbiotic or control preterm microbiota to assess impact on sphingolipids. Fecal content from animals used in Aim 1 will be used to determine the impact of S1P antagonism on the microbiota. Finally, in Aim 3, Dr. Rusconi will combine S1P1 antagonism and dysbiotic preterm microbiota with the NEC-like injury model. She will dissect the role of accumulating lymphocyte populations and altered microbiota on exacerbating NEC-like lesions. Completion of this proposal will provide much needed information on the role of S1P signaling in mucosal immunity establishment and its interplay with the microbiota in the maturing intestine, an interval of life during which NEC occurs. Specifically, this K01 award will allow Dr. Rusconi to improve her ability to plan and conduct animal experiments, refine her immunology skills, and provide her with didactic and practical training in grant writing and manuscript preparation, in a highly mentored environment. Dr. Rusconi?s Institution is supporting her effort with a junior faculty appointment, space, and protected time to perform this work. Her advisory committee consists of her primary mentor Dr. Phillip Tarr, co-mentors Drs. Rodney Newberry and Gautam Dantas, who are investigators with complementary expertise in mucosal immunity, microbe-host interactions, animal models of intestinal disease, and human microbiota modeling. Dr. Rusconi?s Career Development Plan adds to her training in biochemistry, molecular biology, microbiology, and bioinformatics. In summary, this K01 grant will provide Dr. Rusconi the skills to launch an independent research career, amalgamating bioinformatics and experimental biology.